feat: make packages argument required

Cargo.toml

@@ -1,7 +1,9 @@
 [package]
 name = "nish"
+description = "Jump into flake-based nix shells with ease"
 version = "0.1.0"
 edition = "2021"
+license = "MIT"
 
 [dependencies]
 clap = { version = "4.5.17", features = ["derive"] }

src/main.rs

@@ -17,7 +17,7 @@ struct Args {
     /// <package> to implicitly use nixpkgs
     ///
     /// <flake#package> to use a different flake
-    #[arg(value_parser = preprocess)]
+    #[arg(value_parser = preprocess, required = true)]
     pkgs: Vec<Installable>,
 }